There are common problems with most model monitors, but those common problems may be different from one model to the next. Some have common failed caps, some have common failed solder joints, etc, etc.
Your best bet is to describe the problem and give the make/model monitor you're working on to narrow things down a bit. And then the recommended troubleshooting steps can be given.
Recapping a monitor may cure many common problems, but is also just recommended in order to "prevent" problems down the road. Most of these are 20-30 years old now and were run many hours on end, so if it hasn't been done, it's probably due.
I will always cap a monitor if I can tell it has never been done, even if it has nothing to do with the monitors current problem that I'm working on.